[orx-shapes] Add Rectangle.intersection()

orx-shapes/src/commonMain/kotlin/primitives/RectangleIntersection.kt

@@ -0,0 +1,23 @@
+package org.openrndr.extra.shapes.primitives
+
+import org.openrndr.shape.Rectangle
+import kotlin.math.max
+import kotlin.math.min
+
+/**
+ * Find intersection of [this] and [other]
+ * @return a rectangle shaped intersection or [Rectangle.EMPTY] when the intersection is empty.
+ */
+fun Rectangle.intersection(other: Rectangle) : Rectangle = if (this.intersects(other)) {
+    val tn = this.normalized
+    val on = other.normalized
+
+    val left = max(tn.corner.x, on.corner.x)
+    val right = min(tn.corner.x + tn.width, on.corner.x + on.width)
+    val top = max(tn.corner.y, on.corner.y)
+    val bottom = min(tn.corner.y + tn.height, on.corner.y + on.height)
+
+    Rectangle(left, top, right - left, bottom - top)
+} else {
+    Rectangle.EMPTY
+}

orx-shapes/src/jvmDemo/kotlin/primitives/DemoRectangleIntersection01.kt

@@ -0,0 +1,39 @@
+package primitives
+
+import org.openrndr.application
+import org.openrndr.color.ColorRGBa
+import org.openrndr.extra.shapes.primitives.intersection
+
+/**
+ * Demonstrate rectangle-rectangle intersection
+ */
+fun main() {
+    application {
+        configure {
+            width = 720
+            height = 720
+        }
+        program {
+            val h = drawer.bounds.offsetEdges(-100.0, -10.0)
+            val v = drawer.bounds.offsetEdges(-10.0, -100.0)
+
+            extend {
+                drawer.clear(ColorRGBa.WHITE)
+
+                /**
+                 * Find intersection
+                 */
+                val i = h.intersection(v)
+                drawer.fill = ColorRGBa.RED
+                drawer.rectangle(h)
+
+                drawer.fill = ColorRGBa.BLUE
+                drawer.rectangle(v)
+
+                drawer.fill = ColorRGBa.BLACK
+                drawer.stroke = ColorRGBa.WHITE
+                drawer.rectangle(i)
+            }
+        }
+    }
+}